This invention concerns an automatic transmission for a motor vehicle having one starting element, one input shaft, one output shaft, gear sets whose selective engagements by pairs determine different reduction ratios and one planetary reversing gear for reversing the direction of rotation of the input shaft to make possible the reverse gear of the vehicle.
Automatic transmissions are designed as multi-step transmissions or as continuously variable automatic transmissions also called CVT. The latter comprise one starting unit, one forward/reverse gear unit, one variator, one intermediate shaft and one differential. The automatic transmissions are usually driven by an internal combustion engine, via an input shaft, such as the crankshaft. Either a starting clutch or a hydrodynamic torque converter serves as starting unit. The forward/reverse gear unit serves for reversing the direction of rotation of the input shaft for the reverse gear. This unit is mostly designed as a planetary reversing gear. The latter consists of at least one sun gear, several planetary gears, one ring gear, one brake and one clutch of multi-disc design. The variator consists of two cone pulley pairs and one belt-drive organ, each cone pulley pair, in turn, consisting of a first cone pulley stationary in the axial direction and a second cone pulley movable in the axial direction. Between the cone pulley pairs rotates the belt-drive organ such as a pushing linked band. Due to the adjustment of the second cone pulley, the rotor radius of the belt-drive organ changes and thus the ratio of the continuously variable transmission.
The Automobiltechnischen Zeitschrift 96 (1994), No. 6, page 380 has disclosed a continuously variable transmission having one forward/reverse gear unit. One first shaft driven by the impeller of the hydrodynamic torque converter drives the planetary gears connected via a common first planet spider. Each planetary gear is rotatably supported on a pin. On one hand, the planetary gears mesh with a sun gear located upon a second shaft and, on the other hand, with a ring gear. The ring gear can be fixed by a brake of multi-disc design against a stationary wall, such as the transmission housing. The second planet spider is connected by a clutch of multi-disc design with the first cone pulley. When the clutch is closed, the planetary reverse gear rotates as a whole with the ratio 1 and the same direction of rotation as the first shaft. The direction of rotation for the reverse gear is reversed when the brake is closed.
From the Applicant""s DE A 195 15 616 is known a forward/reverse gear unit that comprises one first shaft and one second shaft, one planetary gear, one brake and one clutch. The planetary gear has one sun gear, several planetary gears and one ring gear. The planetary gears respectively sit rotatably upon a pin and are driven via a common planetary spider, the planetary spider being designed integrally with the first shaft. A second planetary spider leads to the inner disc carrier of the clutch, it is possible to design the first and second planet carriers in one piece. The ring gear is connected with an inner disc carrier of the brake. The brake consists of the inner disc carrier, the inner discs, outer discs, one outer disc carrier and one end disc, as a gear tooth system and one piston with recoil device.
The ring gear is integrally connected with a buffer disc and thus supports itself, via the buffer disc, either on a fixed wall or on the first planetary spider. In the forward gear range, no rotational speed difference exists between the ring gear and the first planetary spider. Only in the reverse gear range with a service of about 0.5% does there exist a rotational speed difference between the two parts.
The buffer disc supports itself in the radial direction on one face of the fixed wall. A rotary part, the shaft or the like, can also be considered as a support. The buffer disc can also be radially supported by means of a bearing arrangement.
The ring gear of the planetary reversing set is usually provided on its outer side with a gear tooth system which includes the lining of the discs. The cooling oil is supplied to the discs, via holes, which are partly diagonally placed in the disc teeth. The production of the lube oil holes and also that of the engaging gears is expensive.
The problem on which the invention is based is to simplify the construction of the planetary reversing set of a forward/reverse gear unit of an automatic transmission, especially a continuously variable automatic transmission, so that during the same operation a less expensive production is ensured with optimum operation and, at the same time, the oil supply of the discs is secured under all operating circumstances.
It is provided, therefore according to the invention, that the ring gear consist of one ring with inner teeth and with smooth outer wall and of a disc carrier segmentally welded on the ring.
The disc carrier can be produced inexpensively as a metal plate shaped part without further machining operation. Since the disc carrier is segmentally welded on impressions provided on the joining points with the ring gear, there result between the disc carrier and the ring gear, along the areas between the impressions, gaps through which the lube oil is thrown as result of the centrifugal force on the inner side of the engaging gears of the disc carrier. Th lube oil can be precisely guided to the cooling friction surfaces through oil-passage windows situated between the discs, i.e. in the disc teeth of the disc carrier. The oil-passage windows can be placed by means of the shaping tool at no cost in the disc carrier. Because of the non-machining processing, the oil-passage windows can be placed in the optical axial position, whereas in the prior art, the positions of the oil-passage windows are, in part, predetermined only limitedly by the possible angle and the position of the hole.